Add a bit of infrastructure which will be needed for input filtering:

1) separate filter lists hanging off the r and the c

   requests start off with the same filter list as the connection

   the input filter list is not initialized for subrequests

   internal redirects start off with the same filter list as the
   connection

2) AddInputFilter directive (blatant rip-off of Ryan's AddOutputFilter
   directive); as with AddOutputFilter, the network is implicitly to the
   right of the specified filter list; this may not be the most
   intuitive way to specify the filters; not sure yet


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86403 13f79535-47bb-0310-9956-ffa450edef68